Just spit-balling, but those long-term effects are likely due to the lung damage that the coronavirus incurs on its victims. Ergo, less oxygen = harder for body to work.
That's probably what those sensationalist virus brain damage cases are linked to as well.
It's me! Hindsight! It was from brain inflammation.
Is that so? This virus is more and more mysterious. First it was that antibodies cause lung scarring leading to long term effects and now it's brain inflammation from something that's even harder for the layman to understand.